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Correctly initialise global blocks on Windows. 

Summary:
Windows does not allow globals to be initialised to point to globals in
another DLL.  Exported globals may be referenced only from code.  Work
around this by creating an initialiser that runs in early library
initialisation and sets the isa pointer.

Reviewers: rjmccall

Reviewed By: rjmccall

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D50436

llvm-svn: 339317
This commit is contained in:
David Chisnall 2018-08-09 08:02:42 +00:00
parent 20526bf483
commit c5a458cc53
2 changed files with 44 additions and 2 deletions
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28
clang/lib/CodeGen/CGBlocks.cpp
View File

@ -1213,9 +1213,13 @@ static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
auto fields = builder.beginStruct();
bool IsOpenCL = CGM.getLangOpts().OpenCL;
bool IsWindows = CGM.getTarget().getTriple().isOSWindows();
if (!IsOpenCL) {
// isa
fields.add(CGM.getNSConcreteGlobalBlock());
if (IsWindows)
fields.addNullPointer(CGM.Int8PtrPtrTy);
else
fields.add(CGM.getNSConcreteGlobalBlock());
// __flags
BlockFlags flags = BLOCK_IS_GLOBAL | BLOCK_HAS_SIGNATURE;
@ -1250,7 +1254,27 @@ static llvm::Constant *buildGlobalBlock(CodeGenModule &CGM,
llvm::Constant *literal = fields.finishAndCreateGlobal(
"__block_literal_global", blockInfo.BlockAlign,
/*constant*/ true, llvm::GlobalVariable::InternalLinkage, AddrSpace);
/*constant*/ !IsWindows, llvm::GlobalVariable::InternalLinkage, AddrSpace);
// Windows does not allow globals to be initialised to point to globals in
// different DLLs. Any such variables must run code to initialise them.
if (IsWindows) {
auto *Init = llvm::Function::Create(llvm::FunctionType::get(CGM.VoidTy,
{}), llvm::GlobalValue::InternalLinkage, ".block_isa_init",
&CGM.getModule());
llvm::IRBuilder<> b(llvm::BasicBlock::Create(CGM.getLLVMContext(), "entry",
Init));
b.CreateAlignedStore(CGM.getNSConcreteGlobalBlock(),
b.CreateStructGEP(literal, 0), CGM.getPointerAlign().getQuantity());
b.CreateRetVoid();
// We can't use the normal LLVM global initialisation array, because we
// need to specify that this runs early in library initialisation.
auto *InitVar = new llvm::GlobalVariable(CGM.getModule(), Init->getType(),
/*isConstant*/true, llvm::GlobalValue::InternalLinkage,
Init, ".block_isa_init_ptr");
InitVar->setSection(".CRT$XCLa");
CGM.addUsedGlobal(InitVar);
}
// Return a constant of the appropriately-casted type.
llvm::Type *RequiredType =

18
clang/test/CodeGen/global-blocks-win32.c Normal file
View File

@ -0,0 +1,18 @@
// RUN: %clang_cc1 -fblocks -triple i386-pc-windows-msvc %s -emit-llvm -o - -fblocks | FileCheck %s
int (^x)(void) = ^() { return 21; };
// Check that the block literal is emitted with a null isa pointer
// CHECK: @__block_literal_global = internal global { i8**, i32, i32, i8*, %struct.__block_descriptor* } { i8** null,
// Check that _NSConcreteGlobalBlock has the correct dllimport specifier.
// CHECK: @_NSConcreteGlobalBlock = external dllimport global i8*
// Check that we create an initialiser pointer in the correct section (early library initialisation).
// CHECK: @.block_isa_init_ptr = internal constant void ()* @.block_isa_init, section ".CRT$XCLa"
// Check that we emit an initialiser for it.
// CHECK: define internal void @.block_isa_init() {
// CHECK: store i8** @_NSConcreteGlobalBlock, i8*** getelementptr inbounds ({ i8**, i32, i32, i8*, %struct.__block_descriptor* }, { i8**, i32, i32, i8*, %struct.__block_descriptor* }* @__block_literal_global, i32 0, i32 0), align 4